The present invention relates to syringes and, more particularly, to syringes which are useful in chemical-analysis applications.
In the art of chemical analysis, it is often necessary to be able to take samples of a repeatable, known volume and inject them into analytical instruments. It is further desirous to take samples with an instrument wherein the quality and volume of the sample can be viewed and which is inexpensive so as to be disposable. A conventional instrument to effect such injections is a syringe which is commonly made of plastic or glass with plastic or rubber parts. Such a syringe includes a barrel with a constriction at one end, for containing the sample fluid, and a plunger which is moveable along the inside diameter of the barrel to force the sample fluid through the constriction.
Some sample fluids to be injected consist, however, of highly corrosive liquids or other materials, such as, for example, hydrofluoric, sulfuric, nitric, or chromic acid. Few materials can withstand chemical attack by all such solutions, including glass and stainless steel. Fluorinated polymers, and in particular polymerized tetrafluorethylene resin, available under the name Teflon, a trademark of the DuPont Corporation of Wilmington, Delaware, can, however, withstand chemical attack by such chemicals.
The use of fluorinated polymers having the characteristics of Teflon in syringes presents several problems. Namely, first the cold flow of Teflon tends to cause a loss of seal between the plunger and barrel if they are made of Teflon. Second, flaking from both a plunger and a barrel made of Teflon jeopardizes the integrity of the sample and downstream equipment by contaminating the sample fluid with Teflon particles. Third, Teflon material itself is costly and is difficult to machine.